A physics-based model of flat-band capacitance for metal oxide thin-film transistors

This paper proposes a physics-based model of flat-band capacitance Cfb for metal oxide thin-film transistors, in which the influences of free carriers and electrons trapped in deep/tail states are taken into account. Hereinto, a parameter Ls is introduced to characterize the screening length in the metal oxide semiconductor, which is similar to the extrinsic Debye length (Ld) for conventional MOS structure. Based on the proposed model, the flat-band voltage Vfb can be consequently determined as the gate voltage corresponding to Cgs equal to Cfb. It is shown that the value of Vfb determined by the proposed model is consistent with that extracted from experimental data of I-V and C-V or the simulated results of 2D device simulator ATLAS. Moreover, we investigate the effect of the parameters of density of states on the flat band capacitance and Cgs-Vgs characteristics of metal oxide TFTs by ATLAS in details. It is found that both tail states and deep states should be simultaneously taken into account for determining the flat band capacitance and flat band voltage of metal oxide TFTs. The proposed model for the flat band capacitance of metal oxide TFTs is expected to be useful for device characterization since it is analytical and physically meaningful.